1. Field of the Invention
The present invention generally relates to an authorization system. and in particular to an authorization system using identification information embedded into image data to prevent unauthorized duplication of the image data.
2. Description of the Related Art
Recently, unauthorized copying of digital image data has become a serious problem because duplication of digital data can be extremely easy. To prevent unauthorized copying, several authorization system using identification information (an electronic watermark) embedded into image data have been proposed.
A visible-watermarking system is disclosed in Japanese Patent Unexamined Publication No. 8-241403 which corresponds to U.S. Pat. No. 5,530,759. In this system, a visible, watermark is placed on a digital image such that the corresponding pixel of original image changes its brightness but its chromaticities.
An invisible-watermarking system is disclosed in NIKKEI ELECTRONICS 1996.4.22 (no. 660). In this system, original image data is converted into frequency spectrum and then ID information is embedded into the frequency spectrum which is in turn converted into image data invisibly including the ID information. In authorization check, image data questioned is converted into frequency spectrum. ID information embedded In the image data questioned is obtained from a difference between the frequency spectrum questioned and the original frequency spectrum. Since the ID information is embedded into frequency spectrum of the original image data, it has little effect on the image quality and further it has become very difficult to delete the ID information from the image data.
In the above invisible-watermarking system, since the ID information cannot be seen, it is difficult to check whether image data is authorized in the case where no one knows the ID information. Especially, in a distribution system of data storing medium including CD-ROMs, there are cases where a different watermark is used for each distribution channel. In this case, the authorization check and manufacture management become very complicated and time-consuming jobs.
An object of the present invention is to provide a system which can rapidly check whether image data is authorized to effectively prevent unauthorized copying of the image data.
Another object of the present invention is to provide a system which can easily identify an electronic watermark invisibly embedded in image data to check whether the image data is authorized.
According to an aspect of the present invention, watermarked image data having watermark information invisibly embedded is transferred to a first medium and the embedded watermark information is transferred to a second medium. Since the embedded watermark information is stored in the second medium, watermark identification can be easily made.
Further, in an authorization check system for checking whether a medium questioned is authorized, a storage stores watermark information and medium identification information identifying a medium, the mediums storing watermarked image data which is produced by invisibly embedding the watermark information into original image data. A retrieval controller retrieves watermark information corresponding to medium identification information of the medium questioned from the storage. A watermark extractor extracts watermark information questioned from image data stored in the medium questioned. A checker checks whether the medium questioned is authorized by comparing the extracted watermark information with the retrieved watermark information.
According to another aspect of the present invention, watermarked image data having watermark information invisibly embedded and the embedded watermark information are both transferred to a single medium. Preferably, the embedded watermark information may be stored in a dedicated storage area of the single medium. Further, the embedded watermark information may be encrypted and stored. Since the embedded watermark information is stored in the same medium, watermark identification can be easily made.
Further, in an authorization check system for checking whether a medium questioned is authorized, the medium questioned having a first storage area for storing watermarked image data and a second storage area for storing watermark information. After extracting watermark information from image data stored in the medium questioned, a checker checks whether the medium question is authorized by comparing the extracted watermark information with the watermark information stored in the second storage area of the medium questioned.